Synthesis of hydroxyl-terminated polybutadiene bearing pendant carboxyl groups by combination of anionic polymerization and blue light photocatalytic thiol-ene reaction and its pH-triggered self-assemble behavior

Surface adsorption and solution aggregation of a novel lauroyl-l-carnitine surfactant

HYPOTHESIS

l-carnitine plays a crucial role in the cellular production of energy by transporting fatty acids into mitochondria. Acylated l-carnitines are amphiphilic and if appropriate physical properties were demonstrated, they could replace many currently used surfactants with improved biocompatibility and health benefits.

EXPERIMENTS

This work evaluated the surface adsorption of lauroyl-l-carnitine (C₁₂LC) and its aggregation behavior. The size and shape of the aggregates of C₁₂LC surfactant were studied at different temperatures, concentrations, pH and ionic strength by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Surface tension measurements were carried out to determine the critical micellar concentration (CMC) of C₁₂LC. Combining with the Gibbs equation, the surface excess at different concentrations could be determined. Neutron reflection (NR) was used to determine the structure of the adsorbed layer at the air/water interface with the help of isotopic contrast variations.

FINDINGS

At pH 7, the limiting area per molecule (A_CMC) of the zwitterionic C₁₂LC adsorbed layer at the air/water interface was found to be 46 Å² from surface tension and neutron reflection, smaller than the values of C₁₂PC, C₁₂E₅, DTAB, C₁₂C₄betaine and C₁₂C₈betaine but close to that of SDS. A pronounced surface tension minimum at pH 2 at the low ionic strength was linked to a minimum value of area per molecule of about 30 Å², indicating the competitive adsorption from traces of lauric acid produced by hydrolysis of C₁₂LC. As the concentration increased, area per molecule reached a plateau of 37-39 Å², indicating the dissolution of the more surface-active lauric acid into the micelles of C₁₂LC. DLS and SANS showed that the size and shape of micelles had little response to temperature, concentration, ionic strength or pH. The SANS profiles measured under 3 isotopic contrasts could be well fitted by the core-shell model, giving a spherical core radius of 15.7 Å and a shell thickness of 10.5 Å. The decrease of pH led to more protonated carboxyl groups and more positively charged micelles, but the micellar structures remained unchanged, in spite of their stronger interaction. These features make C₁₂LC potentially attractive as a solubilizing agent.

A novel synthetic strategy for styrene-butadiene-styrene tri-block copolymer with high cis-1,4 units via changing catalytic active centres

A styrene-butadiene-styrene tri-block copolymer (SBS) with a high cis-1,4 unit content (greater than 97%) was synthesized by a novel synthetic strategy based on changing the catalytic active centres using n-butyllithium and a nickel-based catalyst. Firstly, styrene was polymerized via anionic polymerization using butyllithium as the initiator (Li, activity centre Li) at 50°C. The obtained alkylated macroinitiator (PSLi) was aged with nickel naphthenate (Ni) and boron trifluoride etherate (B) to prepare a second reactive centre (Ni-F), which was used to initiate the polymerization of butadiene (Bd). Finally, triphenyl phosphine (PPh₃) was added to adjust the electron density of the third active centre (P-Ni-F), and styrene monomer was added again to synthesize the second polystyrene block to obtain SBS. The polymerization technique presented here is simple and has an efficient initiation effect due to the high initiation activities for the different monomers. It also exhibits excellent control over the stereo-structure of the butadiene segments in the prepared copolymers, and the SBS polymers with high cis-1,4 unit content were easily achieved.

Synthesis of Novel pH-Tunable Thermoresponsive Hydroxyl-Terminated Hyperbranched Polyether

In this study, a new pH-tunable thermoresponsive hydroxyl-terminated hyperbranched polyether (HTHP 2) was successfully prepared via a one-pot cationic polymerization technique and postmodification. In the first step, hydroxyl-terminated hyperbranched polyether containing double bonds (HTHP 1) were synthesized. Then, through thiol-ene "click" reaction, pH-responsive carboxyl groups were introduced to the target polymer of HTHP 2. The products were characterized via Fourier-transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), and size-exclusion chromatography-multiangle laser light scattering (SEC-MALLS). Moreover, dynamic light scattering (DLS) and UV-Vis spectroscopy was employed to study the pH- and thermoresponsiveness in detail. Results showed that HTHP 2 possessed typical pH-controllable thermoresponsive behavior. By regulating the solution pH value range 3.0-5.4, LCST of HTHP 2 could be changed from 12.8 to 68.0 °C. Meanwhile, the cell viabilities of A549 cells were more than 80% for in vitro cytotoxicity tests of HTHP 2, suggested that HTHP 2 polymers are of good biocompatibility for up to 24 h.

A New Strategy for the Synthesis of Hydroxyl Terminated Polystyrene-b-Polybutadiene-b-Polystyrene Triblock Copolymer with High Cis-1, 4 Content

This work reports the preparation of a hydroxyl terminated polystyrene-b-polybutadiene-b-polystyrene triblock copolymer (SBS) with high cis-1, 4 content via a novel nickel catalyst, [η³-Ni(CH₂CHCHCH₂OOCH₃)][BPh^F₄]. FT-IR, ¹H-NMR, and ¹³C NMR indicated that the polybutadiene segment of the copolymer contains greater than 90% cis-1, 4 structure, indicating achievement of the objective. Toward the functionalization goal, a hydroxyl group was successfully introduced at the end of the triblock copolymer (HO–SBS–OH). The results of gel permeation chromatography (GPC) revealed that the polymer is indeed a triblock copolymer, with no traces of homopolymer. Differential scanning calorimetry (DSC) showed that HO–SBS–OH synthesized using the novel catalyst had a lower glass transition temperature (T_g) than HO–SBS–OH synthesized with an alkyl lithium catalyst. Therefore, the polymer synthesized via the novel catalyst contains high cis-1,4 content and displays excellent low-temperature mechanical properties.

Synthesis and Properties of Side-Chain Functionalized Polytetrahydrofuran Derivatives via the Blue-Light Photocatalytic Thiol-Ene Reaction

A series of side-chain functionalized polytetrahydrofuran (PTHF) derivatives were synthesized via the blue-light photocatalytic thiol-ene "click" reaction. Firstly, unsaturated polytetrahydrofuran (UPTHF) as a new unsaturated polyether was synthesized via condensation polymerization of cis-2-butene-1,4-diol and trans-1,4-dibromo-2-butene using potassium hydroxide (KOH) as a catalyst. Then, double bonds in the backbone of UPTHF were modified into different pendant functionality side groups by blue-light photocatalytic thiol-ene "click" reaction using Ru(bpy)₃Cl₂ as a photoredox catalyst, obtaining different side-chain functionalized PTHF derivatives. The structure and the morphology of the side-chain functionalized PTHF derivatives was characterized via Fourier-transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS), and differential scanning calorimeter (DSC). The results showed that the blue-light photocatalytic thiol-ene reaction exhibited high efficiency, and all the unsaturated bonds were modified. Different branch units bestowed different performance of PTHF derivatives; we systematically investigated the thermal properties, pH-triggered and temperature-triggered, self-assembly behaviors of different PTHF derivatives.

A New Synthesis Strategy on Styrene-Butadiene Di-Block Copolymer Containing High cis-1,4 Unit Via Transfer of Anionic to Coordination Polymerization

A novel synthesis strategy on styrene-butadiene di-block copolymer (PS-b-PB) with high cis-1,4 unit content was developed, based on a transfer technique from anionic to coordination polymerization. Firstly, the styrene monomer was initiated by n-butyllithium (Li) utilizing anionic polymerization at 50 °C, which resulted in a macromolecular alkylating initiator (PSLi). Secondly, PSLi was aged with nickel naphthenate (Ni) and boron trifluoride etherate (B) for obtaining a complex catalyst system (Ni/PSLi/B). Then, Ni/PSLi/B was applied to initiate the butadiene (Bd) polymerization. Following this new strategy, a series of PS-b-PBs were successfully synthesized. The experimental results indicated that under the molar ratio combination of [Li]/[Ni] = 5 and [B]/[Li] = 1, styrene-butadiene di-block copolymers could be easily achieved with high cis-1,4 unit content (>97%) and controlled molecular weight as well as narrow molecular weight distribution (Mw/Mn < 1.5). Furthermore, the copolymer's block ratio could also be effectively controlled by controlling the two components' monomer feed ratio.